Composition of matter for the storage of heat



May 4, 1954 M. TELKES 2,577,664

COMPOSITION OR MATTER FOR TRE STORAGE OR HEAT Filed Feb. 19, 1951 IN V EN TOR.

MARIA TELKES Kaufen A TTOR E YS Patented May 4, 1954 UNITED STATES PATNT OFFICE COMPOSITION OF MATTER FOR THE STORAGE OF HEAT 8 Claims.

This invention relates to a composition of matter for use in the storage of heat. This application is a continuation-impart of my copending application Serial No. 693,787, filed August 29, 1946, now Patent No. 2,595,905 issued May 5, 1952.

The invention is not concerned with, or limited to, the storage of heat which has been transmitted from any particular so-urce. Among the applications which have thus far occurred to me are storage of solar heat, storage of waste heat extracted during refrigeration, and the like. For convenience the following description deals with the storage of solar heat.

In the utilization of solar heat for heating purposes, heat collector means and heat storage means are necessary. The heat collector means comprises a radiant energy heat transfer device having at least one radiant energy transferring adapted to absorb incident solar energy in the form of heat. The heat storage means includes a chemical heat storer. The heat storage means is adapted to receive heat from the collector or to deliver it thereto and is arranged in heat transfer relationship with a space the temperature of which is to be controlled.

The use of waste heat extracted during refrigeration for special purposes, such as defrosting, involves storage of heat for considerable periods of time. Effective storage requires that the heat storer chemical shall crystallize freely when heat is given oil and that little or no free Water shall remain when the entire composition has solidie-d, because of the danger of rupture or bursting of pipes and containers. Where, as in the present invention, sodium sulfate serves as the heat storer chemical, it is necessary when giving off heat to prevent or suppress the formation of hydrates (such as the hepta-hydrate, NaaSOMHgO) vv'hich have a different solubility from that of the deca-hydrate. One reason is that formation of hepta-hydrate crystals leaves an excess` of water, which on freezing expands far more than deca-hydrate crystals.

This invention is based upon the discovery that bora-X, when added in amounts between about and 5% to a solution of from about 34% to oi sodium sulfate (anhydrous basis) in water, with or without the addition of a. corro-- sion inhibitor, will have the effect of regulating and controlling the crystallization of sodium sulfate (when giving up heat at its critical ternperature around 90 F.) such that the crystalsy formed are predominantly of the desired decahydrate and of preventing or suppressing the formation ci the undesired hepta-hydrate crystals.

Most materials, and particularly those herein contemplated, when giving; up heat at their critical temperature without any stirring, will undercool below their melting points without crystallization. This can be overcome by stirring or agitation. Since for practical purposes it is desirable to maintain heat storer chemicals in sealed containers to insure long life as Well as to avoid evaporation, direct stirring to prevent undercooling is not possible. Mechanical means for external agitation of the sealed containers oi the chemical while possible is cumbersome and costly. Another object and feature of my invention is thereiore to prevent undercooling in such manner as to avoid the necessity either for rnechanical agitation or stirring, and it therefore permits the use of sealed containers at low cost of operation.

Other objects and novel features of the invention will become apparent from the following specification and the accompanying drawings wherein:

Fig. l is a partial elevational of a heat storage bin in which containers of the heat storage medium are arranged;

Fig. 2 is a vertical section of one of the containers, taken along line 2-2 of Fig. l; and

Fig. 3 is a similar section of a modincation.

In the aforesaid copending application I have described certain heat storer chemicals as particularly suitable for use in heat storage cells or bins and among such chemicals I have mentioned specifically sodium sulfate decahydrate (Glaubers salt) Na2SO4-l0i-I2O as the chemical iiliing substance for the hollow interiors of the storage cells or bins because it meets the requirement ci having a fusion point at or about the temperature at which it is desired to maintain the wall oi the storage cell or bin for use in normal house heating purposes and also has a relatively high latent heat of fusion. Specific constants oi said Glaubers salt are: melting point F. and relatively high heat of fusion of 103 E. t. u. per pound.

In actual practice of the invention it is found that the use of this chemical compound involves careful considerati T and regard for proper conditions for optimum eiiiciency which if disregarded result in poor performance. In my copending application hereinbefore referred to the addition of borax (sodium tetraborate decahydrate) NaaB4Of1-i0H2O was described as appropriate to prevent undercooling ci the Glaubers salt and that it acts also as a corrosion inhibitor.

I have new found that the borax is most eifective when added in speciiic amounts to the Glaubers salt as embodied in the following examples.

Sodium sulfate decahydrate, Glaubers salt, Na2SOi-l0H2O, contains 44% by Weight of sodium sulfate, Na2SO4 and 56% by weight of water H2O. This Glaubers salt can be made readily by mixing anhydrous sodium sulfate NagSOi with water, and as sodium sulfate is available coinrnercially at much lower cost than prepared Glaubers salt, it is preferable from the economic standpoint to utilize the anhydrous sodium sulfate to start.

Furthermore, a solution of anhydrous sodium sulfate NazSOi, saturated at the melting point contains 34% by weight of NaQSOi and 65% by Weight of water. In this, the sodium sulfate is completely dissolved at the melting point, approximately 90 ll'. Since nearly the same amount of heat can be stored in a cubic foot of the saturated solution (34% NagSOi) as can be stored in a cubic foot of Glaubers salt Ne.2SO4.lOi-I2Q (44% NagSOi) the preferred range of the chemical is from approximately 34% by Weight of NazSOi to approximately 44% by weight of NazSOt, taken on an anhydrous basis.

The crystallization promoter borax (sodium tetraborate decahydrate) Na2BiO1..l0H-2O is nixed with the sodium sulfate NaaSOrA plus `,vate the proportion of approximately one to iive per cent by weight of boi-ax and the balance of the Weight is sulfate plus water as described.

The actual preparation of the above composin tion of matter using anhydrous sodium sulfate is as follows:

Water is heated to about 90 F. and one to ve per cent by weight of borax is added thereto as a fine powder.

Optionally, a corrosion inhibitor such as sodium chromate (NazCrOi) or sodium dichromate (NazCrzzOv) or other suitable inhibitors in small quantities, for example, up to approximatel 1/2% by weight is also added to the heated water and both the borax and the selected corrosion inhibitor are dissolved in the water by stirring or agitation. Then from approximately 34% by Weight to 44% by weight of anhydrous sodium sulfate, liaeSOi, are added to the solutions While agitation or stirring continues. if 34% by weight of the sodium sulfate is added, this is dissolved completely, except, of course, for small Quant ties of insoluble foreign matter which may be present in commercial sodium sul l'f more than 34% by weight of anhydrous sodium sulfate is addedL and up to approximately 44% by weight of such. material, the excess above 34% by weight remains insoluble and forms a slurry with the water.

The solution il) containing the sodium sulfate is `then filled into containers Il, preferably of eel and the filled containers i are thereafter aled. If slurry of the type described is present it is necessary to maintain agitation or stirring during nl lng of the containers il to assure uniform dis ribution thereof in the containers ii. Also. dining lling, it is necessary to maintain the temp rature of the material above 90 F. else it orystallizes in part and clogs or plugs the pipes used for :illing the containers. Where containers unaffected by sodium sulfate are used, the corrosion inhibitor may be eliminated.

Examples of my composition of matter follow:

Eample 1 Approximate Weight, pounds Anhydrous sodium sulfate Na2SO4 35 Approximate Weight, pounds Glaubers salt, is used directly instead of the anhydrous sodium sulfate, the composition of matter is prepared by heating the Glaubers salt above its melting point of approximately 98 and boro (and one of the corrosion inhibitors :nef tiene if desired) is then added to the molten Glan salt and mixed together thoroughly. While n eintaining agitation and a temperature above F. the mixture l2 is then introduced into the containers l l which are at once sealed.

Further examples of my composition ol matter are as follows:

Example 3 Approximate weight, pounds Glaubens salt, Na2SO4-10l-I2O 951/2 Borax, NazBiOmlOHzO 3 Corrosion inhibitor 1/2 Total 1GO Example 4 Approximate weight, poun -l Glaubers salt, Na2SO4-l0H2O Borax, Na2B4O7-10H2O 5 Total ico ln the foregoing Examples 1 to 4 inclusive the sodium sulfate (taken on an anhydrous basis) is a percentage of the sum of sulfate and water proximately as follows: in Example l, 9L; Example 2, 42.2%; in Examples 3 and 4, 44 $2. each case the water of crystallization in the horas'. is not counted, since the amounts are small.

In actual use of the compositions o matter consisting of the aforementioned mixtures of any of the examples I have found it most advantageous to fill and sea-l a plurality of individual containers H with such mixtures i0 or l2 and then to provide a plurality of tiers oi such sealed con tainers in a bin B with direct heat transfer contact between the tops Ha of containers il of any tier and the bottoms l lo of containers in the tier at the next upper level. Small spaces i3 are provided for circulation of air or other heat transfer uid between containers in each tier. It is advisable to provide large enough dimensions to the containers Il to allow for eiective heat transfer thereto from the circulatingair or other uid about the containers.

The compositions of matter I have described herein act to store heat and are stabilized as to the conditions under which heat transfer action occurs.

While I have described specic embodiments of the invention, variations in detail thereof are possible and are contemplated. There is no intention, therefore, of limitation to the exact details described.

What is claimed is:

1. A composition of matter consisting by weight of approximately 1% to 5% borax, and the balance essentially all Glaubers salt.

2. A composition of matter as described in claim 1 containing approximately 1/2% of a corrosion inhibitor selected from the group consisting of sodium chromate and sodium dichromate.

3. A heat storage composition consisting by Weight substantially of NazSOi, Water, the NazSOi taken on an anhydrous basis being by weight between approximately 34% and 44% of the sum of the Na2SO4 and Water, and borax by Weight equal to approximately 1% to 5% of the composition.

4. A heat storage composition consisting by Weight substantially of NazSOi, water, the NazSOi` taken on an anhydrous basis being by weight between approximately 34% and 44% of the sum of the NazSOi and Water, borax by weight equal to approximately 1% to 5% of the composition, and approximately 1% of a corrosion inhibitor selected from the group consisting of sodium chromate and sodium dichromate.

5. A heat storage composition comprising by Weight approximately 35% of anhydrous sodium sulfate, approximately 3% borax, approximately 1/2% corrosion inhibitor selected from the group consisting of sodium chromate and sodium dichromate, and approximately S11/2% Water,

A heat storage composition comprising by Weight approximately of anhydrous sodium sulfate, approximately 5% borax and approxi mately Water.

7. A heat storage composition comprising by weight approximately SG1/2% Glaubers salt, approximately 3% borax, and approximately 1/2% corrosion inhibitor selected from the group consisting or sodium chromate and sodium dichromate.

8. A heat storage composition comprising by weight approximately Glaubers salt and approximately 5% borax.

References Cited in the file of this patent UNlTED STATES PATENTS Number Name Date 1,887,618 Bell Nov. 15, 1932 FOREIGN PATENTS Number Country Date 468,756 Germany Mar. 17, 1928 

1. A COMPOSITION OF MATTER CONSISTING BY WEIGHT OF APPROXIMATELY 1% TO 5% BORAX, AND THE BALANCE ESSENTIALLY ALL GLAUBER''S SALT. 